In the manufacture of microcircuits, positive photoresists are used as an intermediate mask for transferring an original mask pattern of a reticule onto wafer substrates by means of a series of photolithography and plasma etching steps. One of the final steps in the microcircuit manufacturing process is the removal of the patterned photoresist films from the substrates. In general, this step is affected by one of two methods. One method involves a wet stripping step in which the photoresist-covered substrate is brought into contact with a photoresist stripper solution that consists primarily of an organic solvent and an amine. However, stripper solutions cannot completely and reliably remove the photoresist films, especially if the photoresist films have been exposed to UV radiation and plasma treatments during fabrication. Some photoresist films become highly crosslinked by such treatments and are more difficult to dissolve in the stripper solution. In addition, the chemicals used in these conventional wet stripping methods are sometimes ineffective for removing inorganic residual materials formed during the plasma etching of metal or oxide layers with halogen-containing gases.
An alternative method of removing a photoresist film involves exposing a photoresist-coated wafer to oxygen-based plasma in order to burn the resist film from the substrate surface in a process known as plasma ashing. Plasma ashing has become more popular in the microcircuit manufacturing process because it is carried out in a vacuum chamber and, hence, is expected to be less susceptible to airborne particulate or metallic contamination. However, plasma ashing is also not fully effective in removing the plasma etching by-products noted above. Instead, removal of these plasma etching by-products must be accomplished by subsequently exposing the photoresist film to certain cleaning solutions. Several commercial products are now available to clean the plasma etching by-products left by plasma etching followed by plasma ashing. For example, EKC 265, available from EKC Technology, Inc., is a post etching cleaning solution composed of water, alkanolamine, catechol and hydroxylamine. Such a composition is disclosed in U.S. Pat. No. 5,279,771 to Lee. ACT 935, available from Ashland Chemical, is another post etching cleaning solution and is composed of water, alkanolamine and hydroxylamine. Such a composition is disclosed in U.S. Pat. No. 5,419,779 to Ward. In both cases, hydroxylamine is used as a corrosion inhibitor. ELM C-30, available from Mitsubishi Gas Chemical, is composed of water, N,N-dimethylformamide, a fluorine compound, organic carboxylate, and a sugar alcohol, wherein the sugar alcohol acts as a corrosion inhibitor. Such a composition is disclosed in U.S. Pat. No. 5,630,904 to Aoyama et al.
These commercial products can effectively dissolve plasma etching residues, however, they can also attack the metallic and oxide layers deposited patternwise on the substrate. This is because the pH of EKC 265 and ACT 935 is above 11 and ELM C-30 contains a fluorine compound. The corrosion inhibitors used in these products are not completely effective in stopping corrosion, because metal layers such as copper, aluminum or aluminum alloys (e.g., Al—Cu—Si), and the like are particularly corrosion sensitive. Furthermore, while the addition of a suitable corrosion inhibitor is essential to prevent corrosion of the substrate metal layers, some corrosion inhibitors tend to inhibit the removal of the plasma etching residue and/or form an insoluble film deposited on the metal substrate surface. Therefore, the corrosion inhibitor must be carefully selected.
It is also difficult to balance effective plasma etching residue removal over corrosion inhibition because chemical compositions of the plasma etching residues are generally similar to those of the metal layers or oxide layers on the substrate. The alkanolamines used in prior art cleaning compositions were oftentimes found to attack the plasma etching residue and the substrate metal layers in the presence of water. Accordingly, there remains a need for a composition that can selectively and effectively remove plasma etching residues without the unwanted attack on the metallic and oxide layers, which causes a loss of metal layers.
Several other patents in the photoresist stripper/cleaner application field exist as follows, although none of them disclose the use of the compositions of the present invention:
Japanese Patent Application No. 7-028254, assigned to Kanto Kagaku, discloses a non-corrosive resist removal liquid comprising a sugar alcohol, an alcohol amine, water, and a quaternary ammonium hydroxide.
PCT Published Patent Application No. WO 88-05813 teaches a positive or negative photoresist stripper containing butyrolactone or caprolactone, quaternary ammonium hydroxide compound, and optionally, a nonionic surfactant.
U.S. Pat. No. 4,239,661 to Muraoka et al. discloses a surface-treating agent comprising an aqueous solution of 0.01% to 20% trialkyl (hydroxyalkyl) ammonium hydroxide. This agent is useful in removing organic and inorganic contaminants deposited on the surface of intermediate semiconductor products.
U.S. Pat. No. 4,904,571 to Miyashita et al. teaches printed circuit board photoresist stripper composition containing a solvent (e.g., water, alcohols, ethers, ketones, and the like), an alkaline compound dissolved in the solvent, including quaternary ammonium hydroxide, and a borohydride compound dissolved in the solvent.
U.S. Pat. No. 5,091,103 to Dean et al. teaches a positive photoresist stripping composition containing: (A) N-alkyl-2-pyrrolidone; (B) 1,2-propanediol; and (C) tetraalkylammonium hydroxide.
U.S. Pat. No. 5,139,607 to Ward et al. teaches positive and negative photoresist stripping composition containing: (A) tetrahydrofurfuryl alcohol; (B) a polyhydric alcohol (e.g., ethylene glycol or propylene glycol); (C) the reaction product of furfuryl alcohol and an alkylene oxide; (D) a water-soluble Bronstead base type hydroxide compound (e.g., alkali metal hydroxide, ammonium hydroxide and tetramethyl ammonium hydroxide); and (E) water. Optionally, the composition may also contain up to 1% of a nonionic surfactant.
U.S. Pat. No. 5,174,816 to Aoyama et al. discloses a composition for removing chlorine remaining on the surface of an aluminum line pattern substrate after dry etching, which composition comprises an aqueous solution containing 0.01 to 15% by weight of a quaternary ammonium hydroxide, such as trimethyl (2-hydroxyethyl) ammonium hydroxide, and 0.1 to 20% by weight of sugar or sugar alcohol, such as xylitol, mannose, glucose and the like.
Other compositions used to strip photoresist include a solution of H2SO4 and an oxidizing agent such as H2O2 that oxidizes, and thus decomposes organic photoresists. However, solutions containing strong acids and oxidizing agents are hazardous to handle, must be applied at elevated temperatures, and require a sufficient amount of hot deionized (DI) water after stripping is performed. Also, such solutions have a short active life as the oxidizing agent readily decomposes. Thus, it is necessary to frequently replenish the solutions. The need for solution replenishment renders the process both hazardous and economically inefficient. In addition, these types of conventional acid-based chemistries are too aggressive on the metal substrates.
Therefore, there remains a need for a new type of cleaning composition for removing plasma etch residues from substrates. Additionally, there remains a need for such a cleaning composition that does not deleteriously affect the substrate. Further, there remains a need for such a cleaning composition that is aqueous-based, non-hazardous and will not harm the environment.